In a vehicle such as an automobile, an airbag apparatus is attached to the inner side of an interior panel covering a portion in front of the front passenger seat or driver's seat thereof. Such an airbag apparatus includes an inflator which is operated in response to an impact at the time of, for example, collision of the vehicle, so as to rapidly inflate and deploy an airbag. By means of pressure generated at the time of inflation and deployment, a fracture opening portion provided on the interior panel is ruptured, and at the same time, the airbag is caused to inflate and deploy toward the outside of the panel through an opening formed as a result of the rupture to thereby protect a passenger sitting in the front passenger seat, or the like, from the impact caused by the collision.
A reinforcement member formed of the same thermoplastic resin material as that of the interior panel is welded to the inner side of the interior panel where such an airbag apparatus is attached; in particular, to the reverse surface of the fracture opening portion of the interior panel. Thus, the reinforcement member prevents the fracture opening portion from concavely deforming or fracturing upon receipt of an impact applied from the outside of the interior panel. In addition, when the fracture opening portion is rupture-opened because of inflation and deployment of the airbag, the reinforcement member prevents the fracture opening portion from separating from the interior panel and scattering. A vibration welding machine is used for such welding between an interior panel and a reinforcement member (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent No. 3043604